Magnetic entrapment for fast, simple and reversible electrode modification with carbon nanotubes: Application to dopamine detection

An electrochemical immunosensor for the detection of Glypican-3 based on enzymatic ferrocene-tyramine deposition reaction

An ultrasensitive electrochemical immunosensor based on signal amplification of the deposition of the electroactive ferrocene-tyramine (Fc-Tyr) molecule, catalyzed by horseradish peroxidase (HRP), was constructed for the detection of the liver cancer marker Glypican-3 (GPC3). Functional electroactive molecule Fc-Tyr is reported to exhibit both the enzymatic cascade catalytic activity of tyramine signal amplification (TSA) and the excellent redox properties of ferrocene. In terms of design, the low matrix effects inherent in using the magnetic bead platforms, a quasi-homogeneous system, allowed capturing the target protein GPC3 without sample pretreatment, and loading HRP to trigger the TSA, which induced a large amount of Fc-Tyr deposited on the electrode surface layer by layer as a signal probe for the detection of GPC3. The concept of Fc-Tyr as an electroactive label was validated, GPC3 biosensor exhibited high selectivity and sensitivity to GPC3 in the range of 0.1 ng mL^-1-1 μg mL^-1. Finally, the sensor was used simultaneously with ELISA to assess GPC3 levels in the serum of clinical liver cancer patients, and the results showed consistency, with a recovery of 98.33-105.35% and a relative standard deviation (RSD) of 4.38-8.18%, providing a theoretical basis for achieving portable, rapid and point of care testing (POCT) of tumor markers.

Theoretical study of interaction of Fe13O8@Zn48O48 cluster with dopamine: Magnetic and optical properties

In this study, we modelled the interaction of Fe₁₃O₈ and Fe₁₃O₈@Zn₄₈O₄₈ (core@shell) cluster with a biologically active dopamine molecule using density functional theory. First, the electronic, magnetic and optical properties of core@shell, Fe₁₃O₈@Zn₄₈O₄₈ cluster investigated and compared with isolated Fe₁₃O₈ and Zn₄₈O₄₈ clusters. Fe₁₃O₈@Zn₄₈O₄₈ cluster is found to be energetically stable. For Fe₁₃O₈ and Fe₁₃O₈@Zn₄₈O₄₈ clusters have the net magnetic moment 42 μ_B. The decrease in HOMO-LUMO gap of core@shell cluster as compared to that of isolated clusters reflects the higher reactivity. The results of the site dependent interaction of Fe₁₃O₈ and Fe₁₃O₈@Zn₄₈O₄₈ clusters with dopamine molecule are presented. The interaction strength is determined in terms of the cluster-dopamine complex binding energy and found to be enhanced for core@shell cluster than the Fe₁₃O₈. Furthermore, the calculated results predict that in presence of dopamine, the magnetic moment of Fe₁₃O₈ and Fe₁₃O₈@Zn₄₈O₄₈ cluster remains unaffected. The analysis of optical spectra of core@shell indicates the obvious red shift compared to Zn₄₈O₄₈ clusters. The optical spectra of Fe₁₃O₈@Zn₄₈O₄₈-dopamine shows the higher oscillator strength as compared to that of Fe₁₃O₈-dopamine complex. Fe₁₃O₈-dopamine complex gives rise to more quenched oscillator strengths as compared to that of bare iron oxide cluster. These results indicate interesting magneto-optical behaviour, which can be useful for biomedical applications.

Detection of Ostreopsis cf. ovata in environmental samples using an electrochemical DNA-based biosensor

Ostreopsis cf. ovata is a benthic microalga distributed in tropical and temperate regions worldwide which produces palytoxins (PlTXs). Herein, an electrochemical biosensor for the detection of this toxic microalga is described. The detection strategy involves isothermal recombinase polymerase amplification (RPA) of the target using tailed primers and a sandwich hybridisation assay on maleimide-coated magnetic beads immobilised on electrode arrays. The biosensor attained a limit of detection of 9 pg/μL of O. cf. ovata DNA (which corresponds to ~640 cells/L), with no interferences from two non-target Ostreopsis species (O. cf. siamensis and O. fattorussoi). The biosensor was applied to the analysis of planktonic and benthic environmental samples. Electrochemical O. cf. ovata DNA quantifications demonstrated an excellent correlation with other molecular methods (qPCR and colorimetric assays) and allowed the construction of a predictive regression model to estimate O. cf. ovata cell abundances. This new technology offer great potential to improve research, monitoring and management of O. cf. ovata and harmful algal blooms.

Interactions of carbon quantum dots from roasted fish with digestive protease and dopamine

The carbon quantum dots from roasted fish interacted with digestive protease and dopamine.

Fabrication of Metal-Substituted Polyoxometalates for Colorimetric Detection of Dopamine and Ractopamine

A novel colorimetric detection method based on the peroxidase-like activity of metal-substituted polyoxometalates (POMs) of SiW₉M₃ (M = Co²⁺, Fe³⁺, Cu²⁺, Mn²⁺) has been established. POMs can catalyze oxidation of dopamine (DA) and ractopamine (RAC) by H₂O₂ in aqueous solutions. SiW₉Co₃-based POMs detect DA at concentrations as low as 5.38 × 10⁻⁶ mol·L⁻¹ simply by observation of the color change from colorless to orange using the naked eye. RAC is detected by observing the change from colorless to slight red by SiW₉Cu₃ with a detection limit of 7.94 × 10⁻⁵ mol·L⁻¹. This study shows that colorimetric DA and RAC detection using SiW₉Co₃ and SiW₉Cu₃ is highly selective and sensitive as well as visually observable.

Mechanical test method and properties of a carbon nanomaterial with a high aspect ratio

Superior nanomaterials have been developed and applied to many fields, and improved characteristic of nanomaterials have been studied. Measurement of the mechanical properties for nanomaterials is important to ensure the reliability and predict the service life times of products containing nanomaterials. However, it is challenging to measure the mechanical properties of nanomaterials due to their very small dimensions. Moreover, macro-scale measurement systems are not suitable for use with nanomaterials. Therefore, various methods have been developed and used to in an effort to measure the mechanical properties of nanomaterials. This paper presents a review of various evaluation systems and the measurement methods which are used to determine the mechanical properties of carbon nanotube (CNT) and carbon nanofiber (CNF), representatively. In addition, we measured the tensile strength and elastic modulus of the CNT and CNF in the scanning electron microscope (SEM) installed the nano-manipulator and the force sensor and this measurement system and results would be introduced in detail.

Reversible nanostructuration of microfluidic electrode devices by CNT magnetic co-entrapment

Carbon nanotubes (CNTs) have been extensively used to produce electrodes of enhanced performance but have only been very recently exploited in microfluidic devices. In these cases, CNT electrodes had to be produced prior to device assembly, which might damage the CNT layer. Here, we show a fast and simple method for the reversible nanostructuration of microfluidic electrode devices in situ. The procedure is based on the attachment of single-walled CNTs (SWCNTs) onto the surface of magnetic particles (MPs) and magnetic confinement of the MP/SWCNT composite onto the sensor in a two-step process that provided homogeneous coating. As it is shown, subsequent magnet removal allows MP/SWCNT release and electrode reutilization. Compared to most previously described methods, ours is faster, simpler and also reversible.

Recent trends in carbon nanomaterial-based electrochemical sensors for biomolecules: A review

Carbon nanomaterials are advantageous for electrochemical sensors because they increase the electroactive surface area, enhance electron transfer, and promote adsorption of molecules. Carbon nanotubes (CNTs) have been incorporated into electrochemical sensors for biomolecules and strategies have included the traditional dip coating and drop casting methods, direct growth of CNTs on electrodes and the use of CNT fibers and yarns made exclusively of CNTs. Recent research has also focused on utilizing many new types of carbon nanomaterials beyond CNTs. Forms of graphene are now increasingly popular for sensors including reduced graphene oxide, carbon nanohorns, graphene nanofoams, graphene nanorods, and graphene nanoflowers. In this review, we compare different carbon nanomaterial strategies for creating electrochemical sensors for biomolecules. Analytes covered include neurotransmitters and neurochemicals, such as dopamine, ascorbic acid, and serotonin; hydrogen peroxide; proteins, such as biomarkers; and DNA. The review also addresses enzyme-based electrodes that are used to detect non-electroactive species such as glucose, alcohols, and proteins. Finally, we analyze some of the future directions for the field, pointing out gaps in fundamental understanding of electron transfer to carbon nanomaterials and the need for more practical implementation of sensors.

Highly Sensitive and Selective Field-Effect-Transistor NonEnzyme Dopamine Sensors Based on Pt/Conducting Polymer Hybrid Nanoparticles

Dopamine (DA), as one of catecholamine family of neurotransmitters, is crucially important in humans owing to various critical effects on biometric system such as brine circuitry, neuronal plasticity, organization of stress responses, and control of cardiovascular and renal organizations. Abnormal level of dopamine in the central nervous system causes several neurological diseases, e.g., schizophrenia, Parkinson's disease, and attention deficit hybperactivity disorder (ADHD)/attention deficit disorder (ADD). In this report, we suggest the fabrication of nonenzyme field effect transistor (FET) sensor composed of immobilized Pt particle decorated conducting-polymer (3-carboxylate polypyrrole) nanoparticles (Pt_CPPy) to detect dopamine. The hybrid nanoparticles (NPs) are produced by means of facile chemical reduction of pristine CPPyNP-contained Pt precursor (PtCl4 ) solution. The Pt_CPPys are then immobilized on an amine-functionalized (-NH2 ) interdigitated-array electrode substrate, through the formation of covalent bonds with amine groups (-CONH). The resulting Pt_CPPy-based FET sensors exhibit high sensitivity and selectivity toward DA at unprecedentedly low concentrations (100 × 10(-15) m) and among interfering biomolecules, respectively. Additionally, due to the covalent bonding involved in the immobilization process, a longer lifetime is expected for the FET sensor.

Fabrication of multiwalled carbon nanotube-surfactant modified sensor for the direct determination of toxic drug 4-aminoantipyrine

A multi-walled carbon nanotube (MWCNT)-cetyltrimethylammonium bromide (CTAB) surfactant composite modified glassy carbon electrode (GCE) was developed as a novel system for the determination of 4-aminoantipyrine(AAP). The oxidation process was irreversible over the pH range studied and exhibited a diffusion controlled behavior. All experimental parameters were optimized. The combination of MWCNT-CTAB endows the biosensor with large surface area, good biological compatibility, electricity and stability, high selectivity and sensitivity. MWCNT-CTAB/GCE electrode gave a linear response for AAP from 5.0×10⁻⁹ to 4.0×10⁻⁸ M with a detection limit of 1.63×10⁻¹⁰ M. The modified electrode showed good selectivity against interfering species and also exhibited good reproducibility. The present electrochemical sensor based on the MWCNT-CTAB/GCE electrode was applied to the determination of AAP in real samples.

Anatase TiO2 based photoelectrochemical sensor for the sensitive determination of dopamine under visible light irradiation

The sensitive photoelectrochemical determination of dopamine was achieved using an indium tin oxide electrode modified with TiO₂ nanoparticles.

Advantageous sensitivity in the DNA homolog of the RNA dopamine aptamer

A competitive enzyme-linked aptamer assay for DA was performed by using two aptamers, individually; one is a 57 mer-RNA aptamer and the other is its homolog DNA aptamer. The difference between the RNA aptamer and the DNA aptamer are based on their particular nucleotides. It is known that the lack of a hydroxyl group in the 2' position of DNA is related with its chemical and biological stability. Thus, the use of the DNA homolog of the RNA aptamer could improve the affinity toward DA due to stability and finally, lower the detection limit. In this paper, we report advantageous sensitivity and specificity of its homolog DNA aptamer assay as compared to the RNA aptamer assay. Both aptamer assays were performed with 0.01 µg mL⁻¹ of each aptamer and 1.205 × 10⁻⁸ M DA-HRP conjugate using the optimized method. A dose-response curve was constructed, and the limit of detection for the DA was determined as 6.3 × 10⁻⁸ M for RNA aptamer assay, and 3.2 × 10⁻¹² M for the homolog DNA aptamer assay, respectively. These results demonstrated that the assay sensitivity was more than 10⁴ times improved with the DNA homolog of the RNA aptamer compared to its original RNA aptamer obtained through SELEX process. Also these results confirmed that the DNA homolog of the RNA aptamer can maintained the binding site and retained a function in both structure. Thus, the switching to the DNA version of RNA aptamer is possible to bind more stably and still able to bind to dopamine.

Nanosheet-based 3D hierarchical ZnO structure decorated with Au nanoparticles for enhanced electrochemical detection of dopamine

A novel sensor based on well-dispersed Au nanoparticles on a nanosheet-based three-dimensionally hierarchical ZnO matrix was fabricated to sensitively detect DA.

Adenosine capped QDs based fluorescent sensor for detection of dopamine with high selectivity and sensitivity

Facile detection of dopamine (DA) in biological samples for diagnostics remains a challenge. This paper reported an effective fluorescent sensor based on adenosine capped CdSe/ZnS quantum dots (A-QDs) for highly sensitive detection of DA in human urine samples. In this assay, adenosine serves as a capping ligand or stabilizer for QDs to render high-quality QDs dispersed in water, and as a receptor for DA to attach DA onto the surface of A-QDs. DA molecules can bind to A-QDs via non-covalent bonding, leading to the fluorescence quenching of A-QDs due to electron transfer. The A-QDs based fluorescence probe showed a limit of detection (LOD) of ca. 29.3 nM for DA detection. This facile method exhibited high selectivity and anti-interference in the presence of amino acid, ascorbic acid (AA), uric acid (UA) and glucide with 100-fold higher concentration in PBS solution. Furthermore, it was also successfully used in the detection of DA in the human urine samples with quantitative recoveries (94.80-103.40%).

High-quality, highly concentrated semiconducting single-wall carbon nanotubes for use in field effect transistors and biosensors

We developed a simple and scalable selective synthesis method of high-quality, highly concentrated semiconducting single-wall carbon nanotubes (s-SWCNTs) by in situ hydrogen etching. Samples containing ~93% s-SWCNTs were obtained in bulk. These s-SWCNTs with good structural integrity showed a high oxidation resistance temperature of ~800 °C. Thin-film transistors based on the s-SWCNTs demonstrated a high carrier mobility of 21.1 cm(2) V(-1) s(-1) at an on/off ratio of 1.1 × 10(4) and a high on/off ratio of 4.0 × 10(5) with a carrier mobility of 7.0 cm(2) V(-1) s(-1). A biosensor fabricated using the s-SWCNTs had a very low dopamine detection limit of 10(-18) mol/L at room temperature.

Carbon nanotube-ionic liquid nanocomposite modified carbon-ceramic electrode for determination of dopamine in real samples

Room temperature 1-butyl-3-methylimidazolium tetraflouroborate ([BMIM][BF4]) ionic liquid was employed for dispersion of multi walled carbon nanotubes (MWCNTs) and the formation of nanocomposite on the surface of a carbon-ceramic electrode. The surface of the modified electrode was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The modified electrode exhibited excellent electrochemical activity to oxidation of dopamine (DA); whereas electro oxidation of ascorbic acid (AA) was not seen and electro oxidation of uric acid (UA) appeared at a more positive potential than DA. The multi walled carbon nanotube-ionic liquid nanocomposite modified carbon-ceramic electrode was used for the selective determination of DA in the presence of high levels of AA and UA using differential pulse voltammetry. The calibration curve for DA was linear in the range of 3.00 to 130 µM with the detection limit (S/N=3) of 0.87 µM. The present electrode was successfully applied to the determination of DA in some commercial pharmaceutical samples and human blood serum.

Spontaneous Deposition of Prussian Blue on Multi-Walled Carbon Nanotubes and the Application in an Amperometric Biosensor

A simple method has been developed for the spontaneous deposition of Prussian blue (PB) particles from a solution containing only ferricyanide ions onto conducting substrates such as indium tin oxide glass, glassy carbon disk and carbon nanotube (CNT) materials. Formation of PB deposits was confirmed by ultraviolet-visible absorption spectrometry and electrochemical techniques. The surface morphology of the PB particles deposited on the substrates was examined by atomic force microscopy and scanning electron microscopy. CNT/PB composite modified glassy carbon electrodes exhibited an electrocatalytic property for hydrogen peroxide reduction. These modified electrodes exhibited a high sensitivity for electrocatalytic reduction of hydrogen peroxide at −0.05 V (vs. Ag|AgCl), probably due to the synergistic effect of CNT with PB. Then, CNT/PB modified electrodes were further developed as amperometric glucose biosensors. These biosensors offered a linear response to glucose concentration from 0.1 to 0.9 mM with good selectivity, high sensitivity of 0.102 A M⁻¹ cm⁻² and short response time (within 2 s) at a negative operation potential of −0.05 V (vs. Ag|AgCl). The detection limit was estimated to be 0.01 mM at a signal-to-noise ratio of 3.

Review on the progress in synthesis and application of magnetic carbon nanocomposites

This review focuses on the synthesis and application of nanostructured composites containing magnetic nanostructures and carbon-based materials. Great progress in fabrication of magnetic carbon nanocomposites has been made by developing methods including filling process, template-based synthesis, chemical vapor deposition, hydrothermal/solvothermal method, pyrolysis procedure, sol-gel process, detonation induced reaction, self-assembly method, etc. The applications of magnetic carbon nanocomposites expanded to a wide range of fields such as environmental treatment, microwave absorption, magnetic recording media, electrochemical sensor, catalysis, separation/recognization of biomolecules and drug delivery are discussed. Finally, some future trends and perspectives in this research area are outlined.